Trim-tab systems have been used for many years to control the attitude of power boats as they move through the water, keeping them as reasonably level as possible. Trim tabs are devices which are adjustably mounted to the transom at the water level and have planar water-engaging surfaces. One tab is typically on the left side of the transom while another is on the right side. The two tabs are well spaced from the drive unit.
Trim tabs typically pivot about a horizontal axis such that their planar surfaces are either raised or lowered to engage the moving water in different ways. In most cases, adjustment of the trim tabs is accomplished by hydraulic means. The hydraulic means for moving a trim tab typically includes either one double-acting cylinder or a pair of single-acting cylinders (one for upward and the other for downward movement) extending between the top of the trim tab and the boat. Bi-direction, uni-directional or rotary pumps may be used in various hydraulic arrangements. In some cases, the drive cylinders have spring returns. Movement means other than hydraulic systems have and can be used, although hydraulic systems are preferred.
Trim tabs are controlled in the typical case by a pair of switches, one for each trim tab. These switches are often double-acting switches. If such a switch is pressed one way it actuates movement of the trim tab in one direction; if pressed the other way it actuates movement in the other direction. The switches are typically beside one another such that both may readily be operated in the same direction at the same time.
Many patents have been used on improvements in trim-tab systems including the following U.S. Pat. Nos.:
4,420,471 (West) PA1 4,644,893 (Zepp) PA1 4,742,794 (Hagstrom) PA1 3,695,204 (Bennett) PA1 4,232,626 (Kern) PA1 3,581,696 (Ilon) PA1 3,628,486 (Bennett) PA1 4,261,278 (Gaudin) PA1 3,641,965 (Schmiedel) PA1 4,718,872 (Olson et al.) PA1 3,577,948 (Frey) PA1 3,589,323 (Kerchival) PA1 3,628,487 (Bennett) PA1 3,760,758 (Banner) PA1 3,814,044 (Kercheval) PA1 3,977,349 (Hummel) PA1 4,597,742 (Finkl).
While trim tabs are widely used and significantly contribute to proper control of power-boat attitudes as they move over the water, a number of shortcomings and problems are present in trim-tab systems of the prior art.
One problem is that some trim-tab control systems do not provide the boat operator a clear indication of the positions of the trim tabs. With many systems it is often necessary to judge the trim-tab positions merely by the perceived attitude of the boat, or even in some cases by moving from the position of control in the boat toward the stern where it may be possible to view the trim tabs.
A variety of trim-tab indicator systems have been developed in the past, including the systems described in the West, Zepp and Hagstrom patents listed above. Some systems of the prior art are electrical or electronic in nature, and have display panels or gauges which may be on or near the dashboard or control panel of the boat. Some systems use a cable system to control a gauge. In such systems, properly controlling movement of the tabs while viewing such may sometimes be difficult. Furthermore, some systems can be susceptible to breakdown from damage to sensitive electrical parts by corrosion or other causes.
Most systems, however, do not have indicators of any kind. In such cases, as well as in some systems having position indicators, the operator often has no knowledge of how fast the trim tabs are moving during adjustment. Therefore, it is often quite difficult to adjust the trim tabs correctly during the first attempt. In some cases, the trim tabs overshoot the intended positions and further attempts at proper adjustment must be made.
There is another significant problem which exists when the operator has no knowledge or insufficient knowledge of the positions of the trim tabs or the rate of their movement during adjustment. The hydraulic system used for trim-tab movement can often be abused or strained by so-called "dead-heading," as attempted adjustment in one direction continues beyond the range of permissible motion. Dead-heading, which involves pumping by a hydraulic pump when no fluid is moving, is prone to occur when the common two-way switch system is used. This can be harmful to the hydraulic equipment.
Improvement is necessary in trim-tab control systems It would be desirable to have a trim-tab control system providing immediate information to the operator about both the position of the trim tabs and how fast they are moving during adjustment.